The present invention relates to compositions including an energy curable fluid vehicle and surface modified, nanometer-sized particles. The inventive compositions have utility in a wide range of applications, but are particularly suitable for use as printing inks, including ink jet printing inks.
Inks are widely used in a variety of printing and coating processes including, for example offset, intaglio, rotogravure, ink jet, flexographic, screen, and spraying techniques. It would be desirable for the inks to remain in a free flowing fluid state during the fluid deposition step, yet undergo rapid self-fixing shortly thereafter to produce durable, non-smearable features on a final receptor material. In many instances, it is desirable to be able to build thickness without substantial spreading of the fluid. The art continuously searches for novel methods to control and improve the rheological characteristics of fluid inks, particularly the rate of self-fixing, which in turn yields better print quality, efficiency and higher speed in the various printing and coating processes.
Ink jet imaging techniques have become very popular in commercial and consumer applications. Ink jet printers operate by ejecting a fluid (e.g., ink) onto a receiving substrate in controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, ink jet printers can produce a wide variety of printed features, including text, graphics, images, holograms, and the like. Moreover, ink jet printers are capable of forming printed features on a wide variety of substrates, including not just flat films or sheets, but also three-dimensional objects as well.
Thermal ink jet printers and piezo ink jet printers are the two main types of ink jet systems in widespread use today. For both approaches, the jetted fluid must meet stringent performance requirements in order for the fluid to be appropriately jettable and for the resultant printed features to have the desired mechanical, chemical, visual, and durability characteristics. In particular, fluids must have relatively low viscosity when jetted, yet must be able to form accurate, durable images on the desired receiving substrate. For example, a typical fluid for thermal ink jetting must typically have a viscosity in the range of 3 to 5 millipascalxc2x7seconds (mPaxc2x7s) at 25xc2x0 C., while piezo ink jet fluids must typically have a viscosity in the range of 10 to 30 mPaxc2x7s at the printhead temperature. The need to use low viscosity fluids (e.g., inks) may make it challenging to obtain printed features with sufficient thickness and resolution to achieve good mechanical, chemical, visual, and durability characteristics.
Phase change inks (e.g., wax based) have been used for a variety of printing processes including piezo ink jet printing. Typically these inks include a dye or pigment mixed with a vehicle made of wax and/or a thermoplastic polymer that is solid at room temperature, but fluid at the printhead temperature (typically greater than 100xc2x0 C.). Since such inks solidify rapidly when printed on the substrate, they give consistent image quality that is independent of the type of substrate used. However, the durability of such phase change ink compositions is typically poor, since they may scratch off easily. This is especially the case when the inks are printed onto non-porous plastic surfaces. Further, due to the waxy nature of the vehicle used in conventional phase change inks, the inks typically have poor adhesion to many substrates.
Organic solvent-based and water-based jettable inks are also well known. A typical water-based ink generally comprises a colorant, which may be a dye and/or a pigment, one or more organic co-solvents, and one or more additives that are included to enhance the performance of the ink. Representative examples of such additives include one or more colorants, slip modifiers, thixotropic agents, tack promoting agents, tack reducing agents, foaming agents, antifoaming agents, flow or other rheology control agents, waxes, oils, plasticizers, binders, antioxidants, fungicides, bactericides, organic and/or inorganic filler particles, leveling agents, opacifiers, antistatic agents, dispersants, and the like.
Printed, and especially ink jet printed compositions also require good dot gain characteristics. Dot gain refers to the degree to which a printed feature spreads out upon application to a substrate. If a printed feature (e.g., a dot or line) spreads out too much on the substrate, the resultant image may tend to have poor resolution. On the other hand, if a printed feature spreads insufficiently upon application to the substrate, then poor image density may result. Dot gain characteristics depend upon factors including the nature of the ink composition, printing conditions, and the nature of the substrate. Some inks show favorable dot gain characteristics on some substrates, but not on others.
It would be desirable to provide ink compositions that have consistently good dot gain characteristics with a wide variety of different porous and nonporous substrates.
It is known that inorganic oxide filler can be incorporated into radiation curable ink compositions in order to increase mechanical and durability properties such as hardness, modulus, abrasion resistance, and refractive index as compared to unfilled systems. The presence of such particles is also believed to decrease not only shrinkage upon curing, but also the coefficient of thermal expansion of the resultant cured composition. Unfortunately, however, incorporating conventional inorganic oxide filler into fluid compositions generally causes the compositions to phase separate, settle, clog printheads during use, lose of optical transparency, and the like with even relatively minor weight loadings of the particles. Such an increase in viscosity is a serious drawback for applications, such as ink jetting, in which relatively low viscosity is necessary for the compositions to be jettable.
Accordingly, it also would be highly desirable to find a way to improve mechanical and durability properties of radiation cured ink compositions without experiencing one or more of the drawbacks of conventional fillers.
The present invention relates to compositions that incorporate surface modified, nanometer sized, inorganic oxide particles into energy curable fluids. The surface modification aspect allows the compatibility between the particles and fluid to be controllably adjusted to achieve a wide range of Theological characteristics. When cured, the presence of the particles also helps improve physical properties such as hardness, modulus, abrasion resistance, refractive index, and the like. The compositions are particularly well-suited for forming printed, radiation cured features on substrates such as paper, signs, walkways, roadways, motor vehicles, boats, aircraft, furniture, equipment, and the like.
Although the compositions are useful in many applications, they are especially useful for ink jet printing applications. The nanometer size of the particles allows the compositions to be ink jetted without clogging the printhead nozzles. The size of the particles is also below light scattering range so that the particles do not interfere with optical clarity or light transparency. Accordingly, although optical additives such as colorants or the like may be incorporated into the formulations, transparent coatings reinforced with the nanometer-sized particles are easily prepared. The surface-treated particles may also be functionalized with energy curable moieties, which allows the particles to react with the energy curable fluid vehicle during curing. This provides the cured compositions with additional reinforcement if desired.
Embodiments of the invention may be formulated with surface modified particles that are only marginally compatible with the fluid vehicle. A wide range of rheological properties can be achieved with this approach. Some embodiments of such compositions are highly thixotropic. The viscosity of the nanocomposite compositions drops dramatically under relatively high shear rates, whereas the viscosity rapidly builds up at relatively low shear rates. This characteristic makes it easy to apply the compositions in the fluid state, while the tendency to thicken after application helps to keep the material in place. Such thermally reversible behavior is useful in many applications, particularly ink jet printing.
For example, in a preferred aspect, the surface modification on the particles may be selected to form compositions that may exist as a gel phase or a fluid phase depending upon the temperature and/or the applied shear rate. By appropriate choice of surface treatment agent(s), either particle-particle or particle-binder precursor interactions can be controllably favored, depending upon the level of energy imparted to the compositions. For example, at room temperature in the absence of shear, sonic, or other energy, such preferred embodiments exist in a gel or other thickened state. Gel formation in particular is believed to result from particle-particle interactions that cause reversible agglomeration of the particles. These particle-particle interactions, however, are weak enough to be broken down by the application of shear energy, sonic energy, heat energy, and/or the like. For example, when heated to about 45xc2x0 C. to about 80xc2x0 C., preferred compositions change from a gel phase to a fluid phase with ink jettable viscosity. When cooled to room temperature, the gel reforms.
This reversible characteristic provides many advantages, including controlled dot gain, enhanced ability to rapidly print fine features, and enhanced ability to build print thickness in ink jet printing. During printing, the compositions are in a low viscosity state. After printing, the compositions quickly thicken or gel (as the case may be) and may be radiation cured to form tough, durable features. The unique Theological properties of the compositions are also useful in screen printing, spin coating, three-dimensional model prototyping, fabricating microelectronic circuits, and other printing applications.
It has also been found that the elasticities of the gel-forming compositions of the invention when shear thinned are much lower than those of conventional shear thinning compositions having comparable viscosities. This leads to very low amounts of stringing, which is advantageous for ink jetting, screen printing, spin coating, and other printing applications.
Consequently, it can be appreciated that the compositions of the present invention offer many advantages for printing applications, especially ink jet printing. Firstly, the compositions can be jetted with a heated ink jet printhead. At moderate temperature, e.g., about 60xc2x0 C., preferred compositions become flowable, preferably substantially Newtonian fluids with a low, ink jettable viscosity. Jetted compositions of the present invention undergo rapid thickening, preferably gelation, on or before contact with a room temperature substrate. The thickening or gel-forming characteristic offers excellent placement control. Printed features have very controllable dot gain, reduced bleed and exceptionally sharp line edges, especially when printed on nonporous substrates. Dot gain has been difficult to control well when some conventional inks have been printed onto nonporous substrates.
The gel character of preferred compositions of the invention offers tremendous control for building print thickness, because the gel materials are much more effective at building print height than fluid materials. This is very desirable in many applications including the fabrication of microelectronic circuits and in fabricating three-dimensional prototypes.
Unlike conventional phase change inks that rely upon waxy materials containing crystalline domains that scatter light and adversely impact transparency, preferred gel-forming compositions of the present invention are optically clear due to small, nanoparticles. Transparent inks and coatings are desirable in many applications, including applying features and/or coatings onto retroreflective substrates for sign applications.
Preferred gel-forming compositions tend to have substantially no yield stress when in the low viscosity state, yet tend to have a measurable yield stress of at least about 0.1 Pascals when gelled. The yield stress of the gel state helps prevent particle agglomeration and settling. Accordingly, the compositions of the invention have excellent storage stability.
Compositions of the invention are not just useful as phase change inks and coatings. For example, the compositions may be used to form covercoats or edge dams on microelectronic devices. Due to the ability to build print thickness so easily, the compositions may also be used for three-dimensional printing in rapid prototyping applications or printing of pressure-sensitive adhesives and/or their radiation-curable precursors.
Other embodiments of the invention may be in the form of relatively low viscosity, substantially Newtonian fluids. These generally result by the use of surface modified particles that have a high degree of compatibility with the fluid vehicle and preferably have energy curable functionality so as to be reactive with the precursor upon curing. The compatibility aspect of the particles has a significant effect upon the rheology of the compositions in that well-dispersed, stable, low viscosity organosols are obtained even with relatively large volume fractions of the particles. Notably, the rate at which the viscosity of these compositions increases with increased particle weight loading is dramatically reduced as compared to systems in which such compatibility is absent.
For example, preferred low viscosity embodiments of the present invention comprising as much as about 10, preferably as much as about 25, volume percent of the particles still retain an ink jettable viscosity over a fairly wide temperature range. This is a remarkable achievement, considering that incorporating only about 5 volume percent of conventional particles, e.g., untreated fumed silica, into a binder precursor renders the compositions too thick to be ink jetted. As an additional benefit, the viscosity characteristics are also substantially Newtonian until relatively high weight loadings of above about 10, preferably up to about 20, volume percent are reached.
The ability to incorporate these highly compatible particles into formulations without an undue increase in viscosity, even with loadings up to about 10 to 25 volume percent, allows cured and uncured compositions of the present invention to enjoy many desired rheological, mechanical, and durability advantages. These advantages include improved hardness, modulus, abrasion resistance, outdoor weatherability, and refractive index. Additionally, the radiation curable reactivity of the preferred particles allows the particles to attachably react with the binder matrix upon curing, resulting in additional reinforcement. Shrinkage upon curing and the coefficient of thermal expansion should also be reduced as compared to an unfilled system.
In one aspect, the present invention relates to a method of forming an ink jetted feature. A composition with an ink jettable viscosity is provided. The composition includes a plurality of nanometer-sized, surface modified, inorganic oxide particles dispersed in an energy curable fluid vehicle. The composition is ink jetted onto a substrate to form a printed feature. The printed feature is exposed to an amount of curing energy under conditions effective to at least partially cure the energy curable fluid.
In another aspect, the present invention relates to an ink jettable composition with reversible gel characteristics. The composition includes an energy curable, fluid vehicle and a plurality of nanometer-sized particles that are marginally compatible with the fluid vehicle and that are present in an amount such that the composition has a gel state and a fluid state in which the composition has an ink jettable viscosity.
In another aspect, the present invention relates to a composition with reversible gel characteristics that includes an energy curable, fluid vehicle comprising a first, relatively polar, constituent and a second, relatively nonpolar constituent. At least one of the constituents is radiation curable. The composition also includes a thickening agent comprising surface treated, nanometer-sized inorganic oxide particles comprising relatively polar and nonpolar surface portions in relative amounts effective to render the thickening agent marginally compatible with the fluid vehicle.
In another aspect, the present invention relates to a method of making an ink jettable composition. An energy curable, fluid vehicle comprising a first, relatively polar, constituent and a second, relatively nonpolar constituent is provided. At least one of the constituents is radiation curable. A gel forming agent also is provided. The gel forming agent comprises surface treated, nanometer-sized inorganic oxide particles comprising relatively polar and nonpolar surface portions in relative amounts such that the gel forming agent is marginally compatible with the fluid vehicle. A gel forming amount of the gel forming agent is incorporated into the fluid vehicle.
In another aspect, the present invention relates to a method of printing. A radiation curable ink is provided that has reversible gel and shear thinned states. The composition is printed onto a substrate to form a printed feature, wherein at least a portion of said printing occurs while the ink is shear thinned. After printing, the printed feature is gelled and then radiation cured.
In another aspect, the present invention relates to a printed feature. The features includes an energy cured binder formed from ingredients comprising an energy curable fluid composition. The composition also includes a gel forming agent dispersed in the binder, said gel forming agent being marginally compatible with the radiation curable fluid composition.
In another aspect, the present invention relates to an energy curable, ink jettable composition. The composition comprises an energy curable fluid vehicle, and a plurality of nanometer-sized particles incorporated into the vehicle. The particles are sufficiently compatible with the vehicle such that the composition has a substantially Newtonian viscosity profile at a desired printhead temperature when the composition incorporates up to at least about 10 volume percent of said particles.
In another aspect, the present invention relates to an energy curable, ink jettable composition. The composition includes an energy curable fluid vehicle and a plurality of nanometer-sized, surface modified, inorganic oxide particles dispersed in the vehicle. The nanometer-sized, surface modified, inorganic oxide particles are sufficiently compatible with the vehicle such that the composition has an ink jettable viscosity at a desired printhead temperature when the composition comprises at least about 10 volume percent of said particles. Additionally, the surface modified particles are obtained by surface treating inorganic oxide substrate particles with a combination of surface treatment agents comprising a first surface treatment agent comprising a radiation curable moiety and a moiety reactively attachable to the substrate particles; and a second surface treatment agent comprising a branched moiety and a moiety reactively attachable to the substrate particles.
In another aspect, the present invention relates to a method of making an energy curable, ink jettable composition. An energy curable fluid vehicle is provided. A plurality of nanometer-sized particles also are provided, and these are sufficiently compatible with the vehicle such that a mixture comprising the particles in the vehicle has an ink jettable viscosity at a desired printhead temperature when the composition comprises at least about 10 volume percent of said particles. Ingredients comprising the particles are incorporated into the vehicle to provide the composition.
In another aspect, the present invention relates to a method of printing. An ink jettable composition is provided that includes a plurality of nanometer sized particles dispersed in an energy curable vehicle fluid. The particles are sufficiently compatible with the vehicle such that a mixture comprising the vehicle and the particles has an ink jettable viscosity at the desired printhead temperature when the mixture comprises at least about 10 volume percent of said particles. The composition is printed onto a substrate to form a printed feature. The printed feature is cured.